"Optimizely is a dedicated AB testing tool and will remove the most effort. GTM can be used for AB testing with some additional configuration effort. Mixpanel supports mobile app AB testing, but web AB testing will require manual configuration. We mostly use Mixpanel with the AB testing when we're looking at complex changes and want to analyze more than just changes in a simple metric or two. If your key pain point is manual effort I'd go with Optimizely."
Hope that helps! We'd be happy to answer any other questions you may have.
Tomasz sent me this in response to your question:
"Optimizely is a dedicated AB testing tool and will remove the most effort. GTM can be used for AB testing with some additional configuration effort. Mixpanel supports mobile app AB testing, but web AB testing will require manual configuration. We mostly use Mixpanel with the AB testing when we're looking at complex changes and want to analyze more than just changes in a simple metric or two. If your key pain point is manual effort I'd go with Optimizely."
Hope that helps! We'd be happy to answer any other questions you may have.
-Cameron